Transmitter-receiver system



May 31, 1949. LABIN 2,471,436

} TRANSMITTER-RECEIVER SYSTEM 2 Sheets-Sheet 1 Filed Jan. 4, 1943 77?.4NSMITT/N I ass/n70: RECEIVER IMPULSE BL OCKNG ENERHTOR DEV/CE 75 RECEIVER IN VEN TOR. E Ml L E L flB/N mom E. LABlN 2,471,436

TRANSMITTER-RECEIVER SYSTEM 2 Sheets-Sheet 2 wuktmub s May 31, 1949.

- Filed Jan.

IN V EN TOR.

EMILE LAB/N 7.

BY fla ATTORNEY .of the impulse transmission. produced by thedissipation of the energy in'the Patented May 31, 1949 UNITED STATES PATENT OFFICE TRANSMITTER-RECEIVER SYSTEM Emile Labin, New York, N. Y., assignor to Federal Telephone and Radio Corporation, Newark, N. J., a corporation of Delaware Application January 4, 1943, Serial No. 471,228

1 Claim. 1 This invention relates to radio transmitter-receiver systems and more particularly to a method and means for blocking the receiver of a radio detection system during the transmission of recurring impulses.

Ordinarily, radio detection systems heretofore proposed use as a blocking pulse for the receiver, pulse energy controlled by the modulating impulse actually applied to the oscillator. In other words, the blocking of the receiver is not commenced until substantially the instant when the high power impulses are radiated. This calls for a very large overvoltage in order to attain a sufficiently rapid blocking action to protect the receiver from the high voltage impulse transmitted. This high blocking potential also requires a time interval proportion-a1 to the amplitude thereof to unblock the receiver. This delay in unblocking the receiver after a high power impulse has been transmitted is one ofthechief difficulties encountered in impulse type of radio detection systems. While the system described relates to radio echo detection systems, the problems occur in other pulse systems wherein alternate transmission an reception is used.

One of the objects of this invention, therefore, is to provide a method and. means for overcoming these disadvantages of prior existing blocking arrangements for radio impulse transmitterreceiver systems.

More particularly, the object of the inventio is to provide a means and method to produce from the transmitter circuit of the radio detection system a low potential blocking pulse which is initiated prior to the occurrence and transmission of an impulse and which can be prolonged for the duration of the impulse transmission.

The method of this invention involves the use of the current flow such as produced in an impulse generator of the kick type disclosed in my Patent No. 2,408,076, dated September 24:, 1946, just prior to and during the occurrence of a generated impulse. The impulse is generated by storing and permitting to dissipate energy in an energy storing device such as an inductance coil and utilizing the flow of energy in such device to render the receiver inoperative. The flow of current due to the storing of energy in the inductance device occurring prior to the transmission of the impulse is used to initiate the blocking of the receiver. By using a circuit with a desired time constant, the duration of the blocking pulse can beextended to cover the duration The current flow 2 coil whereupon the impulse is produced for transmission may also be used to provide a time extension of the blocking pulse. Since the blocking of the receiver is thus initiated prior to the occurrence of the impulse in accordance with my invention, the potential of the'blocking current need not be high. The amplitude of the current may therefore comprise only a part of the total current flow produced during energy storageand dissipation in the energy storage device. The blocking feature of the method may therefore include both a control of the amplitude of the blocking pulse as well as control of the duration of the blocking pulse.

For a better understanding of the method of this invention, reference may be had to the following detailed description of a system by which the method may be practiced, the detailed description to be read in connection With the accompanying drawings, in which,

Fig. 1 is a blockdiagram of a radio detection apparatus embodying the blocking feature of this invention;

Fig. 2 is a schematic illustration of the wiring diagram illustrating the parts of the blocking device and the relationship thereof with respect to the impulse generator of the system; and

Fig. 3 is a graphical illustration showing the relationship of voltage and current in various parts of the circuit illustrated in Fig. 2.

Referring to Fig. 1 of the drawings, a radio .detection system is shown comprising a transmitting oscillator I0, an antenna system l2, and

an impulse generator [4 by which recurring high systems l2 and I8 are preferably of the directive type so that azimuth and elevation of the obstacle can be determined. A blocking device ,2!!! is associated with the generator It to render the receiver non-receptive during the transmission of the high voltage impulses. A radio detection system of this general character is disclosed in the copending application of H. Busignies, Serial No. 381,640, filed March 4, 1941, entitled Position finding system for gun fire control.

The radio detection system in accordance with this invention may include any oscillator and an impulse generator having a current flow just prior to and/or during impulse transmission. For purposes of illustration the oscillator I and impulse generator l4 may be substantially as disclosed in my aforesaid Patent No. 2,408,076. The oscillator disclosed in my aforesaid application includes an inductance coil the use of which involves three distinct operating periods. These periods comprise the storage of energy, dissipation (impulse transmission) and a steady time interval. The steady interval provides a period during which echo pulses can be received on the receiver 16. During the storage and dissipation periods, current is caused to flow in an inductance coil or other energy storing device and it is this current flow which I employ as a blocking current for the receiver l6.

More particularly, the blocking device of this'invention is co-actively associated with the impulse generator [4 as indicated in Fig. 2. The impulse generator is connected as the power supply for the oscillator Ill. The impulse generator M comprises a vacuum tube 22 having a plate 23, a control grid 24 and a cathode 25. An inductance coil 26 is connected in series with a plate circuit 21 and a non-inductance resistance 30 to ground. The cathode is connected to a source of energy B and thence to ground so that in efiect the inductance 26, plate 23, and the cathode 25 are in series arrangement with the source of energy. A positive feed-back between the plate circuit and the grid circuit of the tube is obtained by a coil 28, inductively coupled to the inductance coil 26. The pulsin rate of the generator M is primarily determined by a capacity-resistance timing circuit consisting of a condenser 29 and a resistance 3i. This capacity-resistance circuit is connected in series with the grid 24, and the coil 28, the opposite side of the circuit being connected to the cathode 25.

When energy is being supplied to the inductance 26, that is, when current i flowing in the tube 22, the plate end of the inductance is negative with respect to the terminal end 32 thereof. When energy in the inductance is dissipating (when no tube current flows) the reversed polarity exists.

To the coil terminal 32 I connect the circuit 'of my blocking device 20 which includes the noninductance resistance referred to above.

To this resistance is provided a variable connection 34 to which I connect a time constant circuit including a variable resistance 36 and a condenser 38 connected to ground. The output of this time constant circuit is connected to the appropriate circuits of the receiver IE to provide blocking negative bias therefor during the period of impulse transmission.

will cease to oscillate before energy in the inductance coil 26 is completely dissipated and the high frequency impulse will be a little shorter than that delivered by the inductance coil 26.

The use of inductive coupling between the 4 plate and grid circuits has the effect of shunting the inductance with a negative resistance. For the present purposes the circuit shown in Fig. 2 may be considered during the energy storage period as equivalent to an inductance in parallel with a negative resistance and with the capacities of other components of the circuit.

A circuit consisting of inductance, capacity and resistance, which is capable of oscillating at high values of voltage, may become aperiodic if the resistance is small, even though negative. If Re is the resistance for critical damping, the circuit will be aperiodic as long as the shunt or parallel resistance remains between +Rc and --Rc. When the circuit is made aperiodic by damping with a negative resistance (-Rc), the operation is not at all normal. Any small current increase develops into a very rapid and large exponential increase. From the moment at which the current begins to rise, it continues to rise to its absolute limit, always in the same direction and with increasing speed. Similarly, a decrease in current will also follow an exponential laW.

When energy is being supplied the inductance 26 and this inductance is connected to th oscillator as a plate supply for the tubes thereof, the efiect of the oscillator tubes 42 and 44 may be neglected since, as pointed out above, the polarity of the potential on the inductance is such that the plates of the tubes are at a negative potential with respect to the cathodes and the resistance of the tubes may, therefore, be considered as infinite. When, however, the energy in the inductance is being dissipated, its polarity reverseaand the energy in the inductance dissipates into the tubes as well as the circuit components of the generator itself. During the dissipation, the oscillator tubes act substantially as a resistance load.

The energy dissipation of the inductance begins at the instant that the plate current is blocked. The plate current of the tube 22 having been blocked, the resistance of tube 22 may be considered as infinite, and consequently, the circuit consists of the inductance 26 in parallel with the resistance of the oscillator I0 (if substantially resistive) and a capacity consisting substantially of the capacities of tube 22 and oscillator ID, the distributed capacity of coils 26 and 28, condenser 9 and other capacities to ground. From the theory of parallel inductance, capacity and resistance circuits, it is known that energy dissipation from the inductance 26 into the oscillator (considered as a load) will be made in a minimum time and with a maximum peak power if the circuit constants are given critical values which satisfy the equation.

In Fig. 3, a graphical illustration is given to indicate approximately the current and voltage conditions of certain of the circuit parts shown in Fig. 2. As hereinbefore stated, the cycle of operation T involves three distinct periods. These are indicated as time intervals t1, t2, and is and comprise respectively energy storage, dissipation and steady state periods of operation. This cycle of operation may be described in detail as follows:

Energy storage period As soon as the grid condenser 29 has nearly completed its discharge through the resistance 3], plate current will begin to flow. The plate current as indicated in part a of Fig. 3 increases until a value 50 near saturation of the tube 22 is reached. At the same time, the voltage at the plate 23 will decrease due to the reactance drop across the inductance 26 and the grid voltage (part b) will increase positively due to the feed-back between the grid and plate circuits giving a large grid current flow. The voltage drop 5| (part d) in the plate circuit occurs sharply and then gradually builds up as the plate current approaches the saturation value 50. The grid voltage (part 1)) increases sharply from a negative value to a positive value and as soon as it reaches a positive value, grid current (part c) commences to flow. During this charging period, the plate voltage approaches the voltage of the plate supply 52 and the grid voltage reaches a positive maximum while the grid current remains substantially constant.

Energy dissipation period When the plate current saturation 50 is reached, energy in the inductance 26 dissipates producing a maximum of voltage 54 and the grid voltage suddenly becomes negative and the flow of grid current is stopped. The flow of plate current will then become less, the effect becoming cumulative causing the plate current to decrease rapidly. The grid voltage decreases and finally becomes negative. The result is that the flow of plate current will be stopped in a very short time producing a high voltage at the terminals of the inductance 26. If the coupling of the coils 26 and 28 is properly adjusted, a high regative voltage 55 approximately equal to the instantaneous plate voltage 54 will be produced at the grid 24, and this negative voltage will be sufiicient to block the plate current during the discharge of the inductance 26. The dissipation of energy from the coil 26 occurs the instant when current stops flowing through the plate circuit 21. This discharge is applied to the plate circuit of the tubes 42 and 44 of the oscillator 10.

Steady period After dissipation of energy in the inductance 26, all of the currents and voltages except the grid voltage assume their steady state value, the grid voltage reaching its steady state value only after the discharge of the grid condenser 29. During storage of energy in the inductance 26, the grid current of the tube 22 charges the condenser 29 with such polarity that the plate of the condenser connected to the grid 24 will be negative. At the end of the energy dissipation of the inductance 26, there will be no voltage across the coil 28 and therefore, due to the negative charge of the condenser 29, plate current will not flow. The condenser, however, will complete its discharge through the resistance 3| by the end of the time interval is and plate current will again how and the cycle will repeat.

As shown in part e, Fig. 3, the current flow 60 tapped off at 34 during the period of energy storage in the inductance 26 is similar in shape to the plate current (part a) with the exception that the current 60 is negative. The energy dissipation current of the inductance 26 tapped 01f at 34 is indicated by the curve 6|. The currents 60 and GI combine to produce a current pulse 62. The current pulse 52 as indicated covers the periods t1 and 152.

This pulse I use to block the receiver during the transmission of the high voltage impulse 54. The time constant feature of the resistance 36 and condenser 38 operates to extend the duration of the impulse where it is desirable to have the receiver blocked off a longer time interval. The variable contact 34 also controls the amplitude of the blocking pulse. Proper adjustments of the contact 34 and the variable resistance 36 may be used to effect pulse amplitude and pulse duration as indicated by the broken lines 64 and 66 (part e).

It will be readily apparent from the foregoing disclosure that the low voltage blocking feature of my invention overcomes the disadvantages of the high power blocking pulses heretofore used. It will also be appreciated that the control of the amplitude of the duration of the blocking pulse is another desirable and important feature of this invention.

While I have described these features in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of my invention as set forth in the objects of my invention and the accompanying claim.

What I claim is:

A radio-transmitter-receiver system, comprising a transmitter, an associated receiver, an impulse generator including a thermionic device having a plate, a grid and a cathode, an oscillatory circuit including an inductance connecting said grid and cathode, a circuit for supplying negative blocking pulses to said receiver, including timing elements, an inductance element coupled to said first named inductance for receiving energy therefrom having one end connected to said plate and to said transmitter and the other end to said blocking pulse supplying circuit, whereby corresponding positive pulses are supplied to said transmitter and negative ones to said pulse supplying circuit, said negative pulses being supplied ahead of the corresponding positive ones to block the receiver.

ElVIILE LABIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 827,524 DeForest July 31, 1906 1,916,016 Rives June 27, 1933 2,050,418 Boerner Aug. 11, 1936 2,055,883 Terry Sept. 29, 1936 2,199,179 Koch Apr. 30, 1940 2,256,539 Alford Sept. 23, 1941 2,408,076 Labin Sept. 24, 1946 

